Scotland centre Alex Dunbar could miss the Rugby World Cup – after collapsing with suspected ligament damage to his left knee in training on Thursday.

Dunbar had been named in the XV to face England in Saturday's Calcutta Cup clash at Twickenham.

But, running on his own just an hour before selection was announced this morning, he changed direction and his knee simply gave way. The damage is being scanned at a private hospital in Edinburgh, while a specialist will need to examine the images before making a final diagnosis.

Alex Dunbar faces a race against time to be fit for the Rugby World Cup after injuring his knee at training

While Scotland coaching staff are hopeful that he may only have torn his cartilage, putting him out of action for around six weeks, there is a real fear that Dunbar has sustained damage to his ACL – which means up to six months on the sidelines.

Matt Scott, who had been due to start on the bench, will take Dunbar's place in the starting line-up on Saturday.

Scotland centre Dunbar was due to start against England in the Calcutta Cup on Saturday

David Denton, Jim Hamilton and Dougie Fife will all start for Scotland against England on Saturday after Vern Cotter made five changes to his starting XV.

Stand-off Finn Russell also returns to the Dark Blues line-up for the penultimate RBS 6 Nations clash at Twickenham after suspension ruled him out of the 22-19 defeat to Italy at Murrayfield two weeks ago.

The Scots are desperate to restore pride in the Calcutta Cup meeting following three straight defeats to France, Wales and the Azzurri.

Edinburgh number eight Denton - the only player among the incoming five not to have featured in this year's competition - replaces Johnnie Beattie after shaking off the calf strain which has kept him out of action so far.

Denton's Gunners team-mates Fife - a try-scorer against France in round one - and Matt Scott replace injured wing Sean Lamont and centre Alex Dunbar, who are both ruled out with knee complaints.

Russell, meanwhile, starts in place of Peter Horne while experienced Saracens lock Hamilton takes the place of benched forward Tim Swinson.

Cotter said: 'Jim comes in and will bring his physicality and understanding of English rugby to our forward pack.

'It's good to have Dave Denton back as he provides us with strong ball-carrying and strong defence. He's also a very good lineout forward and will give us a bit more physical density against a big forward pack.

'It's been tough on Finn to sit out and it's great to have him back. He's slotted straight back in to the structure we're looking for.

'Finally, Dougie came on and played well against France and has had a couple of games with his club.

'We're looking for him to bring his enthusiasm, energy and high work-rate, particularly in kick-chase and receipt.'

Tighthead prop Euan Murray, meanwhile, will equal Allan Jacobsen's all-time appearance record for a Scotland prop when he collects his 65th cap.

Dunbar, here showing his disappointment after Scotland's loss to Wales, awaits results of scans on his knee

He will partner Alasdair Dickinson and fit-again Ross Ford, who has recovered from the back spasm suffered against Italy to start in an experienced front-row.

Jonny Gray remains in the second-row to pack down with Hamilton, while Blair Cowan and Rob Harley start together for the sixth consecutive time in the back-row, alongside Denton.

Captain Greig Laidlaw will again partner the returning Russell from scrum-half, with the back-line completed by Glasgow Warriors trio Mark Bennett, Tommy Seymour and Stuart Hogg.

'It will be played away from home at a very intense level and will allow us to assess further our ability to operate away from home in a hostile environment.

'Our focus, however, has been on ourselves and how we can perform better, by identifying the areas that we can control - like improving our skill sets and reinforcing our cohesion - to withstand the difficult times and also apply some pressure.'